setSecurityRealm

Defines a security realm and adds defined users to it. If a user has specified the standard
ServletPropertySet.USERS property, then we try and turn these into an in-memory default
realm, and then set that realm on all of the webapps. TODO: this is not ideal. We need a way
to specify N named realms to the server so that individual webapps can find their appropriate
realms by name.